ISIS seems to have struck again: A video released by the terrorist organization depicts a man hovering over the severed head of Peter Kassig, who was kidnapped last year in Syria. The act marks the fifth Western hostage murdered by ISIS. In the video, the executioner threatened the United States, saying ISIS will soon “begin to slaughter your people in your streets.”

What’s most disturbing is that Kassig was in Syria for humanitarian work, providing relief supplies for the thousands of refugees in the area. Peter started his own small organization with his savings, providing aid buying supplies for Syrian refugees.

This summer, before his death, he wrote a letter to his parents in which he highlighted how frightened he was: “I am obviously pretty scared to die, but the hardest part is not knowing, wondering, hoping, and wondering if I should even hope at all.” President Obama described the killing as “pure evil.”

The motivation for these killings by groups such as ISIS is both monetary and what they believe is a form of retaliation.

Just like any organization, Al Qaeda and ISIS rely on a steady supply of revenue to continue their operations. Because European countries in particular are more likely to pay, these groups consistently focus on capturing more of their hostages. Some countries such as France and Italy regularly make ransom payments to retrieve their hostages. The monetary value of these transactions is not small. In July, the New York Times calculated that Al Qaeda’s revenue stream derived from ransom payments is approximately $125 million.

In contrast, the American policy is to never make ransom payments under any circumstances. This very policy in many ways led to the death of Kassig.

Given the many Republican victories in the midterm elections, there is strong reason to believe that the United States will toughen its strategy against ISIS. John McCain, the incoming chairman of the Senate Armed Services Committee, has said since “at least” the end of the Cold War, ISIS is the greatest threat the United States faces.

The increased violence by the ISIS will also likely trigger a new Authorization for the Use of Military Force. The authorization was initially passed in 2001 that specifically allows the military to go after people, groups, and countries that had a part in the 9/11 attacks. By drafting and signing a new authorization specifically targeting the ISIS, Obama would be given more power in using military force.

A senior Kurdish leader has recently provided intelligence for the number of soldiers in the ISIS ranks. At 200,000 militants, the number is seven to eight times larger than previous CIA estimates. The larger army has allowed the terrorist organization to fight on two fronts simultaneously, in northern Iraq and in Syria. If accurate, this will mean that the United States will have a very difficult time beating ISIS through air attacks alone.

The Daily Iowan Editorial Board believes that ISIS represents an imminent national-security threat. While it can sometimes lead to killings such as that of Kassig, the United States should pressure European countries to adopt similar no-ransom policies to cut off the revenue these countries provide to terrorist groups. Congress should also work with the president to institute a new authorization so the United Staters can target ISIS more effectively. If the number of radical militants really is as high as recent intelligence suggests, the United States should be open to the possibility of a “boots on the ground” operation in order to eradicate this terrorist organization.